1. Field of the Invention
The invention relates in general to a method for adjusting a control parameter and an optical disc drive server system using the same, and more particularly to a method and a device, which are adopted in a control loop of an optical disc drive server system and for inputting a sinusoidal signal to the control loop in an open loop manner so as to obtain the control parameter of the control loop.
2. Description of the Related Art
FIG. 1 is a block diagram showing a conventional optical disc drive servo system. As shown in FIG. 1, an optical sensor 102 receives an optical signal reflected from the disc (not shown), converts the optical signal into an electric signal, and outputs the electric signal to a pre-amplifier 104 to obtain a tracking error signal/focus error signal Te/Fe. The tracking error signal/focus error signal Te/Fe processed by an ADC (Analog to Digital Converter) 106 is inputted to a compensator 108, which compensates for a gain and a phase thereof. The compensated tracking error signal/focus error signal Te/Fe is processed by a DAC (Digital to Analog Converter) 110, and then a signal Tro/Foo is obtained. The signal Tro/Foo is inputted to a driving circuit 114 so that a control signal T/F for controlling a position of an optical pickup 116 is generated. The laser diode (not shown) of the optical pickup 116 generates a laser beam to read/write the disc. It is to be noted that the ADC 106, the compensator 108 and the DAC 110 may be designed in the same ASIC 112.
However, after the optical disc drive has operated for a long period of time, the system's physical property is changed owing to the temperature variation. That is, the gain of the control loop 120 constituted by the driving circuit 114, the optical pickup 116, the optical sensor 102 and the pre-amplifier 104 is changed and makes the system unstable. The system's unstable state influences the disc reading/writing operations.
The conventional optical disc drive overcomes the system's unstable condition by two methods. The first method is to additionally dispose a temperature sensor in the system in order to sense the temperature variation. Then, the gain variation of the control loop 120 may be estimated according to the temperature variation. This method, however, cannot obtain the precise gain variation, and the improvement to the system's unstable condition is thus limited. In addition, the extra component increases the cost of the optical disc drive. The second method is to reduce the reading/writing speed of the optical disc drive for the purpose of reducing the error in reading/writing. However, this method cannot really solve the problem of gain variation.